The present invention relates to a torque detection method for a vehicular internal combustion engine, and a hydraulic control method for an automatic vehicular transmission to which the torque detection method can be applied suitably.
In a control method disclosed in U.S. Pat. No. 3,754,482, for example, an operating oil pressure to be supplied to transmission control clutches (frictional engagement elements) during transmission control of an electronically-controlled automatic transmission is adjusted by detecting the valve opening of a throttle valve and the car speed and applying electricity of a predetermined quantity, based on the detected values, to a solenoid for operating oil pressure control. In such a prior art automatic transmission, the detected values of the throttle valve opening and the car speed cannot always be parameters which accurately indicate the input transmission torque for the transmission. Thus, it is impossible to ensure smooth and speedy transmission control without a shock.
Disclosed in the above-mentioned U.S. Pat. No. 3,754,482, moreover, is a control method in which the changing rate of the input shaft speed of a transmission during transmission control is detected, and the pressure supplied to a connection- and/or release-side clutch is feedback-controlled so that the detected rate agrees with a target changing rate. According to the feedback control of this type, however, if a drastic change of the throttle valve opening during the transmission control cannot be followed up with good responsiveness, the changing rate of the input shaft speed, and hence, the output torque, suffer hunting, thus failing to permit smooth transmission control. Unless the level of the pressure (initial value) supplied to the clutches at the start of the transmission control is proper, moreover, hunting is liable to be caused.
In order to avoid such an awkward situation, it is necessary to detect the instantaneous value of the input shaft torque of the transmission and use the detected value for hydraulic control of a clutch for transmission control.
In a conventional method for detecting the torque of a power transmission input shaft, the torque is detected by means of a strain gage or magnetostriction. Sensors used for such detection are large-sized, and the detected value is subject to a great thermal effect. Also, the detection of the torque of the rotating shaft requires use of a slip ring, which entails problems on reliability and costs.
The torque value may be obtained in the following manner. The engine torque values corresponding to the throttle valve openings and the engine speeds are mapped in advance, and the torque is calculated in accordance with detected values of the valve opening and the engine speed based on the stored map values. According to this method, however, it is hard or impossible to cope with deterioration of engine performance and change of engine temperature (engine water temperature). In engines with a supercharger, such as a turbocharger, moreover, the engine torque cannot be accurately detected in accordance with only the throttle valve opening and the engine speed, due to a time lag during rapid acceleration.
Alternatively, the torque value may be obtained in the following manner. The engine torque values corresponding to the injection quantities and the intake-air quantities are mapped in advance, and the torque value is calculated in accordance with detected values of the injection quantity and the intake-air quantity based on the stored map values. According to this method, however, if the friction loss of a crankshaft or the like changes, the calculated torque value will be subject to errors. Substantial errors may be also caused depending on the engine temperature.